rehernden Messages: 20 Registered: February 2014 Location: Blairsville, Ga
Junior Member
Came across this on CL so drove 100 miles to go get it.
Sounds nice except for the hiss. Been reading the forum here for the past couple days and will try some of the "fixes" to see if I can quiet it down a little bit. Previous owner has already done the three prong power cord, and replaced the speakers with Eminence Delta 15-B's. Speaker jack is labeled Jensen.
First I'll try de-soldering the blue wires at driver board to try to isolate where hiss is coming from. Also there is a pulsating hum on the normal side. Could this maybe be the big filter caps?
I'm no electronic tech but reasonably confident I can de-solder and replace transistors etc if I can determine which ones need it. Trying to figure out the different part numbers is a little confusing. Has anyone considered making some "sticky" posts with FAQ's and maybe a clear part # cross reference and where they are located on schematic for newbies such as myself?
Anyway, thanks for a great site I would be totally lost without it.
pleat Messages: 1452 Registered: June 2004 Location: Belding, Mi
Senior Member
Congrats on the amp and cab. Photo looks like it's in nice shape. Can't help you much on the hum, but when the speakers were replaced, they may not have ordered 16 speakers as replacements. If they are 8 ohms you would have a 2.6 ohm total load to the head. The K200 amps want a 4 ohm total load for the full rated output. Going below the 4 ohm may damage the amp.
rehernden Messages: 20 Registered: February 2014 Location: Blairsville, Ga
Junior Member
Yea, I was a little concerned about the ohm rating. After looking on the Eminence website the Delta 15-B only showed 16ohm. Cannot find a rating on the actual speakers. Previous owner had them wired parallel but the top speaker went thru a capacitor or resistor that looks factory. I guess the Jensen's that were in there had a different horn or something in the top position? I bypassed that and just have them standard parallel for 5.33ohm. Thanks for the welcome, will probably have some other questions along the way.
Kustom_Bart Messages: 601 Registered: October 2010 Location: Greenville, MichiGUN
Senior Member
Is the capacitor about as big around as your thumb and about 2 1/2-3" long? if so then it was meant for a siren horn as the crossover and used to be a siren cabinet. It would of had 2 15" speakers in the bottom two holes and then a spun aluminum horn in the top hole. They work great for PA mains set up that way. I have a pair with Altec speakers in them.
rehernden Messages: 20 Registered: February 2014 Location: Blairsville, Ga
Junior Member
Maybe not quite that big, should have written down the number. This is before I bypassed it.
Here's one of the speakers, couldn't find any ohm rating on them so have to trust their website. They sound good.
On another note. I read that some people replace the filter caps with 10,000uf 50v but may have to upgrade the bridge rectifier also. Would it make sense to just put in a couple 6500uf 50v and not have to change bridge rectifier. Not sure I need to do this yet but just thinking ahead a little.
rehernden Messages: 20 Registered: February 2014 Location: Blairsville, Ga
Junior Member
Had a chance to play thru this rig today. sounds nice, everything works, don't notice the hiss when playing. When pushed kinda hard, guitar volume about 80 percent, amp volume at 1:00, plucking low a, e, or g notes pretty hard the bottom speaker farts a bit. can't really blame that on the amp. These speakers sell for $100 each so maybe that's all they can handle. Normally don't play that loud so no worry's and having second thoughts about replacing any transistors etc. Now just need to get a coiled cord for the complete 70's vibe.
stevem Messages: 4733 Registered: June 2004 Location: NY
Senior Member
If you want the best sound from that amp if you are playing bass
You really need to get ports into the cabinet!!
In stock form the 3-15 cabinets are far two small for 3-15s, (heck the 2-15 cabs are border line to small) to sound there best even with the stock size ports.
For those delta 15b`s are looking for 7.20 cubic ft of cabinet volume each.
In short those cabinets need a minimum of 4 stock size ports, with at least two it will fart out less on the low E string.
Oh,sorry I forgot,welcome to the place!
rehernden Messages: 20 Registered: February 2014 Location: Blairsville, Ga
Junior Member
Hmm, didn't think about that. It has four 2 1/2" ports behind the grill cloth already. Wouldn't be hard too make four more and give it a try. Thanks for that idea.
stevem Messages: 4733 Registered: June 2004 Location: NY
Senior Member
You need to have tubes behind them even if they do not pass out thru the grill cloth.
Parts express sells kits to make up the lenght tubes you need.
Another option is to make slot type ports on the bottom and top of the baffel.
rehernden Messages: 20 Registered: February 2014 Location: Blairsville, Ga
Junior Member
Wow! There's a lot of math and science involved to determine port size, location, and tube length. Apparently it is easy to make matters worse is done incorrectly. I'll have to find an online calculator and study this a little bit.
pleat Messages: 1452 Registered: June 2004 Location: Belding, Mi
Senior Member
All good points on the port tubes and such, but it won't make a kustom cab sound like a new computer designed cab. From what I've read, your using the system for guitar. One thing you may want to try first is to make sure that the baffle board is bolted tightly to the cabinet. Over time the nuts may have worked loose. I'd also make sure that each speaker, the nuts are snug evenly. Since you mentioned only the bottom speaker is farting out, it may be the speaker is not evenly secure to the baffle board. On cabinets I've boughten over the years that the grill cloth is dusty or drinks spilled on them. I remove the baffle board, head to the car wash and power wash and rinse them. Vacuum off the excess water, and let them dry in the sun for a hour or so. Brings the grill cloth to factory fresh and allows me to make sure all nuts are secure when I reassemble the cab.
pleat
According to this calculator I need 2.19" for 45hz for the four ports that are already there. 6.21"-45hz if I put four more ports. Of course it changes with different hz. This is for 2.5" dia ports.
Does this sound about right? 45hz seems to be inline with the eminence speakers.
I use this for bass guitar. The grill cloth was kinda dusty, cleaned it up best I could but the car wash idea would be better. I checked all the nuts when the back was off and they were tight. Wonder if the baffle board is really needed with these different speakers.
Kustom_Bart Messages: 601 Registered: October 2010 Location: Greenville, MichiGUN
Senior Member
s far as the bridge rectifier, do not mess with a Kustom amp unless it is giving you problems. They are not amps that you dive into and just start replacing parts unless they need it. This amp will last a very long time as you will never turn it up loud enough to hurt the head, you will hurt yourself first....lol! They are the opposite of tube amps that you have to piddle with all the time.
rehernden Messages: 20 Registered: February 2014 Location: Blairsville, Ga
Junior Member
Yea, volume at 12:00 seems to be plenty. Haven't decided yet if I'm going to replace any transistors to remove some of the white noise, really it is no louder than the fan on my SWR sm400s head. Will probably experiment on the cabinet some to see if I can get rid of the bottom speaker distortion since it's no longer "original" with the new speakers.
stevem Messages: 4733 Registered: June 2004 Location: NY
Senior Member
The first transistor after the input jacks on each preamp board would be the place to start as the noise from these transistors gets amped up hundreds if times by the gain stages on down stream.
With a cost of some 50 cents for two of them you can scrape that up from your cars under seat area!
rehernden Messages: 20 Registered: February 2014 Location: Blairsville, Ga
Junior Member
That's funny, I'm gonna go out right now and check my car. Thanks. I read one of your other post's about the first three transistors. Gonna practice on an old circuit board first then may give it a try for real.
pleat Messages: 1452 Registered: June 2004 Location: Belding, Mi
Senior Member
I'd move the bottom speaker that is causing some issues to the top position and the top speaker to the bottom. If the issue stays in the bottom position, then you have some cabinet issues. If the issue follows the speaker, then you have a speaker that will need to repaired.
pleat
Kustom_Bart Messages: 601 Registered: October 2010 Location: Greenville, MichiGUN
Senior Member
I agree with Pleat 100%. It may be a speaker problem and not a cabinet problem.
My dad owned a service station and wrecker service for 35 years and you would be amazed what I would find under the seats of wrecked cars. I began working there when I was 10 or so years old. When he hauled in a wreck we were liable to clean out any personal property, so that was my job, I would box it up for the owners to pick up. Then I got to search the car under the seats etc, after it was turned over to us. I have found everything from diamond rings to condoms....lol! once a 100 dollar bill too. LOL! However, it was nothing to find 6.00 or more in change under the rear seat.
rehernden Messages: 20 Registered: February 2014 Location: Blairsville, Ga
Junior Member
After closer exam discovered all three eminence speakers are suffering from over excursion. Took the back off so I could see what they were doing and made it worse of course.
So as an experiment I made some block off plates for the port holes and it helped a little but since these delta 15-b speakers only have 1.6mm xmax they just can't seem to handle the power this amp puts out. Found some other speakers with twice the xmax but just one would cost almost as much as I paid for this whole rig.
As for the amp. Went ahead and bought some new transistors but could not bring myself to cut the two blue wires to see where the white noise is coming from. Only original once except for the replacement 3 prong power cord so guess I'll live with the hiss for now. Don't know if keeping the circuit boards original will help resale value years from now or not.
stevem Messages: 4733 Registered: June 2004 Location: NY
Senior Member
The 100 watts of rms power from the amp should not drive even just one of those speakers to xmax unless those drivers had been in a different cabinet for sub use and drivin to death!
rehernden Messages: 20 Registered: February 2014 Location: Blairsville, Ga
Junior Member
Yea that's what I thought too since they are rated at 400 watts each but I think that is what's happening. They sound like little hammers when push to hard, from what I've read that's what over excursion sounds like. Also tried putting some port tubes on tuned to 40hz with no change. Maybe you're right and they have been abused in the past some time, they sound great otherwise.
pleat Messages: 1452 Registered: June 2004 Location: Belding, Mi
Senior Member
Have you tried the amp with a different speaker cabinet or the kustom cabinet with a different amp head to see if the problem stays with the cab or follows the amp head?
pleat
rehernden Messages: 20 Registered: February 2014 Location: Blairsville, Ga
Junior Member
I have a 4x10 4ohm cab I'll try it with and a another amp to try with the kustom cab to see how it goes.
In the meantime I went ahead and cut the two blue wires with no change in the white noise which I guess means it is coming from the power amp. So changed the four 36892 transistors mounted in a row on the bottom of amp with 2n3055's location Q1-Q4 on the schematic I think. Pretty easy with no soldering, put some new heat sink compound on and it seems to have reduced the noise by maybe a third, not very scientific but it does seem a little quieter. Everything I've read so far says there will always be some white noise so not sure about trying anything else or not.
stevem Messages: 4733 Registered: June 2004 Location: NY
Senior Member
Kustom used 4 matched outputs for low crossover distortion levels, if your amp now sounds like its got a horrible distortion to it when played up near its full RMS power level thats why.
If thats the case you can swap those 4 new ones around from place to place and see if it gets better.
stevem Messages: 4733 Registered: June 2004 Location: NY
Senior Member
They may be the same part number but that's no guaranty that they will all pull the same idle current , or have the same gain so to speak.
Play it loud and give it a listen, you will hear if it's got nasty distortion or not compared to what it sounded like with the original outputs.
rehernden Messages: 20 Registered: February 2014 Location: Blairsville, Ga
Junior Member
Okay gotcha.
Tried my SWR amp with the kustom cab and it sounds about the same, so I don't know. Can dial back the bass and it's not as bad and probably shouldn't be playing that loud anyway, but get carried away sometimes
rehernden Messages: 20 Registered: February 2014 Location: Blairsville, Ga
Junior Member
Finally got around to testing the speakers with 9 volt battery. They move somewhere between 1/16" and 1/8" kinda hard to judge the distance but doesn't look like more than 1/8". While in there removed the port block off plates and put port tubes back on tuned to 38hz if my calculations are correct. Really can't tell any difference in overall sound with or without the tubes in place. It is louder though without the plates on there.
Now that the white noise is isolated to the power amp (by cutting blue wires) would it make since to replace the transistors located at Q1-Q4? Is it really possible to remove all the white noise from these amps?
I'm not sure I know which transistors you are referring to so I don't have an answer for you on that one. The hiss can be caused by transistors or resistors or capacitors. Each case is different. The hiss is generated more in earlier stages of the amp where the gain factor is large and less in the final output stage where the gain is less.
You can make these amps quieter, but all amps will have some background hum and hiss. How loud is it compared to your other amps?
rehernden Messages: 20 Registered: February 2014 Location: Blairsville, Ga
Junior Member
Sorry, I take that back about Q1-Q4 I think those are the transistors mounted on the bottom of chassis and I have done those but remember there being 6 of them. Reading the schematics is a bit over my head.
The hiss is really not all that bad, is more than my Carvin PB500 which is nearly silent, but less than the cooling fan on my SWR SM400s, this SWR used to have a pretty bad hiss but had a tech fix it with a new signal path whatever that is. If I stood further away the Kustom probably would not notice it so much.
I don't mean to draw this thread out too long and appreciate everyone's input. I may have come across a k300 pa amp and cabs and may have some questions about that if I end up with it.
The 4 large transistors on the bottom are the output transistors. On a K200B there should be 4 on an aluminum extrusion that also has the bias diode and the thermal cutoff switch connected to it.
There are two additional large transistors on the power amp board that are part of the low voltage regulator circuit.